The effect of grazing management on the hydrological balance of natural pastures on the North-West Slopes of New South Wales

Abstract

Natural pastures, which are dominated by native plant species, occupy an extensive proportion of Australia (432 M ha, or 56% of the continental landmass). Traditional grazing methods (continuous set-stocking) can lead to low levels of herbage mass, litter mass and ground cover, which in turn leads to high surface runoff, high soil evaporation, and poor pasture growth. A key component of designing a sustainable grazing system for these pastures includes a sound knowledge of the impact of that system on the hydrological balance. A grazing management experiment was established at Springmount near Barraba on the North-West Slopes to study the effect of five grazing treatments on pasture characteristics while monitoring the associated impact on selected components of the hydrological balance. The grazing treatments included: continuous grazing (4 and 6 sheep/11a), continuous grazing with subterranean clover and fertiliser applied (8 sheep/ha), and rotational grazing (4 sheep/ha) with pastures grazed for four weeks and rested for four weeks (two paddock rotation) or rested for 12 weeks (four paddock rotation). The continuous grazing treatments had significantly lower mean levels of herbage mass (1500-1800 kg DM/ha), litter mass (1)0-110 kg DM/ha) and ground cover (70-73%) compared with either rotational grazing or over-sowing with subterranean clover (3000-3500 kg DM/ha, 210-260 kg DM/ha, and 83-90% for herbage mass, litter mass and ground cover, respectively).